Efficiency thermoelectrics utilizing thermal isolation

ABSTRACT

An improved efficiency thermoelectric system and method of making such a thermoelectric system are disclosed. Significant thermal isolation between thermoelectric elements in at least one direction across a thermoelectric system provides increased efficiency over conventional thermoelectric arrays. Significant thermal isolation is also provided for at least one heat exchanger coupled to the thermoelectric elements. In one embodiment, the properties, such as resistance or current flow, of the thermoelectric elements may also be varied in at least one direction across a thermoelectric array. In addition, the mechanical configuration of the thermoelectric elements may be varied, in one embodiment, according to dynamic adjustment criteria.

REFERENCE TO PRIOR PROVISIONAL APPLICATION

This Application is related to and claims the benefit of the filing dateof prior filed U.S. Provisional Patent Application No. 60/267,657 filedFeb. 9, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improved thermoelectrics for producingheat and/or cold conditions with a greater efficiency.

2. Description of the Related Art

Thermoelectric devices (TEs) utilize the properties of certain materialsto develop a thermal gradient across the material in the presence ofcurrent flow. Conventional thermoelectric devices utilize P-type andN-type semiconductors as the thermoelectric material within the device.These are physically and electrically configured in such a manner thatthe desired function of heating or cooling.

Some fundamental equations, theories, studies, test methods and datarelated to TEs for cooling and heating are described in H. J. Goldsmid,Electronic Refrigeration, Pion Ltd., 207 Brondesbury Park, London, NW25JN, England (1986). The most common configuration used inthermoelectric devices today is illustrated in FIG. 1. Generally, P-typeand N-type thermoelectric elements 102 are arrayed in a rectangularassembly 100 between two substrates 104. A current, I, passes throughboth element types. The elements are connected in series via coppershunts 106 soldered to the ends of the elements 102. A DC voltage 108,when applied, creates a temperature gradient across the TE elements.FIG. 2 for flow and FIG. 3 for an object both illustrate generaldiagrams of systems using the TE assembly 100 of FIG. 1.

When electrical current passes through the thermoelectric elements, oneend of the thermoelectric elements becomes cooler and the other endbecomes warmer. TE's are commonly used to cool liquids, gases andobjects.

The basic equations for TE devices in the most common form are asfollows: $\begin{matrix}{q_{c} = {{\alpha \quad I\quad T_{c}} - {\frac{1}{2}I^{2}R} - {K\quad \Delta \quad T}}} & (1)\end{matrix}$

 q _(in) =αIΔT+I ² R  (2) $\begin{matrix}{q_{h} = {{\alpha \quad I\quad T_{h}} + {\frac{1}{2}I^{2}R} - {K\quad \Delta \quad T}}} & (3)\end{matrix}$

where q_(c) is the cooling rate (heat content removal rate from the coldside), q_(in) is the power input to the system, and q_(h) is the heatoutput of the system, wherein:

α=Seebeck Coefficient

I=Current Flow

T_(c)=Cold side absolute temperature

T_(h)=Hot side absolute temperature

R=Electrical resistance

K=Thermal conductance

Herein α, R and K are assumed constant, or suitably averaged values overthe appropriate temperature ranges.

Under steady state conditions the energy in and out balances:

q _(c) +q _(in) =q _(h)  (4)

Further, to analyze performance in the terms used within therefrigeration and heating industries, the following definitions areneeded: $\begin{matrix}{\beta = {\frac{q_{c}}{q_{i\quad n}} = {{Cooling}\quad {Coefficient}\quad {of}\quad {Performance}\quad ({COP})}}} & (5) \\{\gamma = {\frac{q_{h}}{q_{i\quad n}} = {{Heating}\quad {COP}}}} & (6)\end{matrix}$

From (4); $\begin{matrix}{{\frac{q_{c}}{q_{i\quad n}} + \frac{q_{i\quad n}}{q_{i\quad n}}} = \frac{q_{h}}{q_{i\quad n}}} & (7)\end{matrix}$

 β+1=γ  (8)

So β and γ are closely connected, and γ is always greater than β byunity.

If these equations are manipulated, conditions can be found under whicheither β or γ are maximum or q_(c) or q_(h) are maximum.

If β maximum is designated by, β_(m), and the COP for q_(c) maximum by,β_(cm), the result is as follows: $\begin{matrix}{\beta_{m} = {\frac{T_{c}}{\Delta \quad T_{c}}\left( \frac{\sqrt{1 + {Z\quad T_{m}}} - \frac{T_{h}}{T_{c}}}{\sqrt{1 + {Z\quad T_{m}}} + 1} \right)}} & (9) \\{{\beta_{c\quad m} = \left( \frac{{\frac{1}{2}Z\quad T_{c}} - {\Delta \quad T}}{Z\quad T_{c}T_{h}} \right)}{{where};}} & (10) \\{Z = {\frac{\alpha^{2}}{R\quad K} = {\frac{\alpha^{2}\rho}{\lambda} = {{Figure}\quad {of}\quad {Merit}}}}} & (11) \\{T_{m} = \frac{T_{c} + T_{h}}{2}} & (12)\end{matrix}$

and;

Wherein:

λ=Material Thermal Conductivity; and

ρ=Material Electrical Resistivity

Note that for simple solid shapes with parallel sides, K=λ×area/length.Similarly R=(ρ×length)/area. Thus, any change in shape, such as a changein length, area, conality, etc., can affect both K and R. Also, if theshapes of flexible elements are changed by mechanical or other means,both K and R can change.

β_(m) and q_(cm) depend only on Z, T_(c) and T_(h). Thus, Z is named thefigure of merit and is basic parameter that characterizes theperformance of TE systems. The magnitude of Z governs thermoelectricperformance in the geometry of FIG. 1, and in most all other geometriesand usages of thermoelectrics today.

For today's materials, thermoelectric devices have certain aerospace andsome commercial uses. However, usages are limited, because systemefficiencies are too low to compete with those of most refrigerationsystems employing freon-like fluids (such as those used inrefrigerators, car HVAC systems, building HVAC systems, home airconditioners and the like).

The limitation becomes apparent when the maximum thermoelectricefficiency from Equation 9 is compared with C_(m), the Carnot cycleefficiency (the theoretical maximum system efficiency for any coolingsystem); $\begin{matrix}{\frac{\beta_{m}}{C_{m}} = {\frac{\frac{T_{c}}{\Delta \quad T}\left( \frac{\sqrt{1 + {Z\quad T_{m}}} - \frac{T_{h}}{T_{c}}}{\sqrt{1 + {Z\quad T_{m}}} + 1} \right)}{\frac{T_{c}}{\Delta \quad T}} = \left( \frac{\sqrt{1 + {Z\quad T_{m}}} - \frac{T_{h}}{T_{c}}}{\sqrt{1 + {Z\quad T_{m}}} + 1} \right)}} & (13)\end{matrix}$

Note, as a check if Z→∞,β→C_(m). The best commercial TE materials have Zsuch that the product;

ZT_(a)≈1

Several commercial materials have a ZT_(a)=1 over some narrowtemperature range, but ZT_(a) does not exceed unity in presentcommercial materials. This is illustrated in FIG. 4. Some experimentalmaterials exhibit ZT_(a)=2 to 4, but these are not in production.Generally, as better materials may become commercially available, theydo not obviate the benefits of the present inventions.

Several configurations for thermoelectric devices are in current use forautomobile seat cooling systems, for portable coolers and refrigerators,for high efficiency liquid systems for scientific applications, for thecooling of electronics and fiber optic systems and for cooling ofinfrared sensing system.

All of these devices have in common that the T_(h) is equalized over thehot side of the TE, and similarly, T_(c) is equalized over the coldside. In most such devices, the TEs use an alumina substrate (a goodthermal conductor) for the hot and cold side end plates and copper oraluminum fins or blocks as heat exchangers on at least one side.

Thus, to a good approximation, conditions can be represented by thediagram in FIG. 5. In this case ΔT has been split into the cold side atΔT_(c) and hot side ΔT_(h) where ΔT=ΔT_(c)+ΔT_(h).

Using (1) and (2) in (5): $\begin{matrix}{\beta = {\frac{q_{c}}{q_{i\quad n}} = \frac{{\alpha \quad I\quad T_{c}} - {\frac{1}{2}I^{2}R} - {K\quad \Delta \quad T}}{{\alpha \quad I\quad \Delta \quad T} + {I^{2}R}}}} & (14)\end{matrix}$

But ΔT is the sum of ΔT_(c) and ΔT_(h). So, for example, ifΔT_(c)=ΔT_(h) then ΔT=2ΔT_(c). Since the efficiency decreases withincreasing ΔT, it is highly desirable to make ΔT as small as possible.One option is to have the fluid flowing by the hot side be very largecompared to that by the cold side. For this case, the equation for heatflow from the hot side is:

q_(h)=C_(p)MΔT_(h)  (15)

where C_(p)M is the heat capacity of the fluid passing the hot side perunit time (e.g., per second).

Thus, if C_(p)M is very large for a given required q_(h), ΔT_(h) will bevery small. However, this has the disadvantage of requiring large fansor pumps and a large volume of waste fluid (that is, fluid not cooled,but exhausted as part of the process to achieve more efficient cooling).

A second option is to make the heat sink on the hot side very large sothat the heat is dissipated passively. Examples would be a low power TEin a car with the hot side in very good thermal contact with the vehiclechassis, or a TE system in a submarine with the TE in good thermalcontact with the hull and hence, the ocean water. In general, however,these methods are difficult to implement or cost, weight, size or otherconditions limit their use. The result is that ΔT is substantiallylarger than ΔT_(c) in most devices, and efficiency suffers accordingly.

SUMMARY OF THE INVENTION

In general, an improved efficiency thermoelectric device is achieved bysubdividing the overall assembly of thermoelectric elements intothermally isolated sub-assemblies. Overall efficiency may be improved byutilizing the thermal isolation, and controlling the positioning anddirection of the flow of the material to be cooled or heated throughportions of the thermoelectric device. Efficiency may also be improved,by varying ΔT, and physical, thermal and electrical properties ofportions of the overall thermoelectric device.

One aspect of the present invention involves a thermoelectric system foruse with at least one medium to be cooled or heated. The system has aplurality of thermoelectric elements forming a thermoelectric array witha cooling side and a heating side; wherein the plurality ofthermoelectric elements are substantially thermally isolated from eachother in at least one direction across the array. At least one heatexchanger is provided on at least one of the cooling and/or the heatingsides and in thermal communication with at least one thermoelectricelement. The heat exchanger is configured to significantly maintain thethermal isolation of the thermoelectric elements.

In one embodiment, the medium, such as fluid, solids or a combination ofboth, moves across at least a portion of at least one side of the array,in at least one direction. In another embodiment, at least onecharacteristic, such as resistance, of the thermoelectric elements isvaried in the direction of medium movement. Resistance may be varied ina number of ways, such as variation of length of the thermoelectricelements, variation of cross-sectional area of the thermoelectricelements, variations in the mechanical configuration of eachthermoelectric element, or through resistivity of at least onethermoelectric material, and in any manner appropriate to theapplication.

In yet another embodiment, the current through the thermoelectricelements is different for at least some thermoelectric elements in thearray.

Advantageously, the heat exchanger comprises a plurality of portions,such as posts, fins, or heat pipes, each portion in thermalcommunication with at least one thermoelectric element, at least some ofthe portions substantially thermally isolated from other of saidportions in the direction of medium movement. Preferably, the thermalisolation of the portions corresponds to the thermal isolation of thethermoelectric elements, thereby providing significantly thermallyisolated sub-assemblies. In one embodiment, a heat exchanger is providedon each of the cooling and the heating sides. Alternatively, one sidehas a heat sink and one side has a heat exchanger. The heat sink may becoupled to one side of the thermoelectric array via a heat pipe that isin thermal contact with the array at one end and with a heat sink at theother end. In another embodiment, the thermoelectric elements are alsosubjected to at least one magnetic field.

Advantageously, at least one characteristic of the thermoelectric systemis dynamically adjustable through adjustment of the mechanicalconfiguration of the thermoelectric system. A control system coupled tothe thermoelectric system may adjust the mechanical configuration basedupon at least one input to the control system. Preferably, the controlsystem operates to improve efficiency dynamically through theadjustment. An algorithm may be provided in accordance with which thecontrol system operates. In one embodiment, the control system adjustsat least one characteristic based upon at least one input to the controlsystem.

The various features, such as thermal isolation, variation of acharacteristic, variation of current, provision of magnetic fields andcontrol systems may be used in various combinations, or alone, forparticular applications.

Another aspect of the present invention involves a method of making athermoelectric system for use with at least one medium, such as a fluid,solid or combination of fluid and solid, to be cooled or heated. Themethod involves the steps of forming a plurality of thermoelectricelements into a thermoelectric array with a cooling side and a heatingside; wherein the plurality of thermoelectric elements are substantiallythermally isolated from each other in at least one direction across thearray, and exchanging heat from at least one side of the thermoelectricarray in a manner that significantly maintains the thermal isolation ofthe thermoelectric elements.

In one embodiment of the method, the medium is moved across at least aportion of at least one side of the array in at least one direction.Another embodiment of the method involves the further step of varying atleast one characteristic, such as resistance or mechanical configurationof the thermoelectric elements in the direction of medium movement. Forexample, resistance could be varied in any number of ways such asvarying the length, the cross-sectional area, the mechanicalconfiguration, or the resistivity of at least some of the thermoelectricelements. In one embodiment, the step of varying comprises dynamicallyadjusting the at least one characteristic. Preferably, the adjustment isin response to evaluation of at least one parameter from a sensory inputor by a user. An algorithm may be followed to control the adjustment.

In one embodiment, the step of exchanging heat involves providing a heatexchanger comprising a plurality of portions, each portion in thermalcommunication with at least one thermoelectric element, at least some ofthe portions substantially thermally isolated from other portions in thedirection of medium movement. The portions may take on any number ofconfigurations such as posts, fins, or heat pipes, or other suitableheat exchanger materials. In one embodiment, the step of exchanging heatinvolves exchanging heat on both the cooling side and the heating side.Alternatively, the method involves the step of sinking heat from atleast one side of the thermoelectric array.

In another embodiment, the method further involves the step of varyingthe current through at least some thermoelectric elements in the array.In yet another embodiment, the method further involves the step ofsubjecting the thermoelectric elements to at least one magnetic field.

These and other features of the present invention are described infurther detail below in connection with a number of Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The below Detailed Description of the Preferred Embodiments is made inconjunction with the following figures.

FIGS. 1A and 1B depict a conventional thermoelectric device;

FIG. 2 depicts a conventional thermoelectric device in a conventionalfluid heating or cooling application;

FIG. 3 depicts a conventional thermoelectric element for use in coolinga material or component;

FIG. 4 depicts an efficiency measure of various thermoelectricmaterials;

FIG. 5 illustrates a generalized conditions diagram of conventionalthermoelectric devices;

FIG. 6 illustrates a generalized block diagram of a thermoelectricsystem;

FIG. 7A depicts a first embodiment of a thermoelectric system inaccordance with the present invention and its accompanying temperatureprofiles;

FIGS. 7B and 7C depict a more detailed illustration of the constructionof the thermoelectric system of FIG. 7A;

FIGS. 7D and 7E depict alternative embodiments of the thermoelectricsystem of FIG. 7A, including additional enhancements according to thepresent invention;

FIG. 8 depicts a thermoelectric system in accordance with the presentinvention for flow from opposite sides;

FIGS. 9A-9E depict examples of thermoelectric devices incorporating thefeatures of FIGS. 7A-E and FIG. 8, but utilizing different geometriesfor the heat exchangers and thermoelectric elements;

FIG. 10 shows another embodiment of a thermoelectric system inaccordance with the present invention using a control system, whichvaries the current through various portions of the system.

FIG. 11 illustrates yet another embodiment of a thermoelectric system inaccordance with one aspect of the present invention, in which aresistance change in the thermoelectric elements is achieved bymechanical means;

FIG. 12 shows yet another embodiment of the thermoelectric system inaccordance with the present invention in which efficiency is furtherenhanced by virtue of the application of magnetic fields;

FIG. 13 illustrates yet another embodiment in which the efficiency isfurther enhanced by the virtue of a magnetic field across the length ofthe TE elements;

FIG. 14 depicts an illustration of a thermoelectric system in accordancewith the present embodiment, where the material to be cooled is a solidrather than a fluid;

FIGS. 15A-15G illustrate various examples of temperature profiles alongthe length of an isolated element thermoelectric system in accordancewith the present invention;

FIG. 16 illustrates yet another embodiment of a thermoelectric system inwhich the flow on the waste side traverses the length of thethermoelectric array in sections;

FIG. 17 illustrates yet another embodiment of a thermoelectric system inwhich flow on the waste side traverses the length of the array insections, but differs from FIG. 16 in that the flow is from oppositeends;

FIG. 18 illustrates yet another embodiment of a thermoelectric system inwhich flow on the waste side does not traverse the entire length of thearray.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is introduced using examples and particularembodiments for descriptive purposes. Although a variety of examples arepresented to show how various configurations can be employed to achievethe desired improvements, the particular embodiments are onlyillustrative and not intended in any way to restrict the inventionspresented.

A generalized block diagram of an overall TE system 600 is shown in FIG.6. A thermoelectric assembly 601 with hot side 603 and cool side 604 iselectrically connected to a power source 602. The thermoelectricassembly 601 is in good thermal contact with a hot side heat exchanger607 on the hot side 603 and with a cool side heat exchanger 608 on thecool side 604. Equipped with suitable ducts or pipes, sources of fluid605 for the hot side 603 and 606 for the cool side 604, send theirfluids through their respective heat exchangers 607 and 608. Heatedfluid 609 and cooled fluid 610 exit the system at the right in thefigure. For certain applications (with examples given below) one of theheat exchangers 607 or 608 may be replaced with a heat sink therebyeliminating the need for a fluid source or fluid on that side.

In general, and as described in further detail throughout thisspecification, the present invention relates to improving efficiency inthermoelectric systems by enhancing the thermoelectric systemconfiguration to provide thermal isolation between elements or stages ofa thermoelectric system along the array in the direction of flow for amedium to be heated or cooled. The bulk of the examples below areprovided with a focus on cooling. However, the principles haveapplication to heating, as well. One illustration of a first embodimentof a TE system 700 that substantially improves efficiency in accordancewith the present invention is depicted in FIG. 7A. As illustrated, a TEelement array 701 is constructed with a hot side substrate 702 and acool side substrate 703 sandwiching a plurality of TE elements 704. Aplurality of pins 705 are in good thermal contact with the TE elements704, via both the hot side substrate 702 and the cool side substrate703, and form heat exchangers for the TE system 700. As shown, the pins705 have a form very similar to nails, with their heads 706 in goodthermal contact with the TE elements 704 (hot and cold side).Preferably, the pins 705 are constructed of copper or other materialhaving high thermal conductivity. Depending upon the application or thefluids to which heat transfer takes place, the pins 705 may be replacedwith other heat exchanger configurations or geometries. Some suchgeometries are described below, such as heat pipes or fins. The heatexchanger should minimize heat transfer in the direction of fluid flowfrom pin to pin while maintaining good heat transfer from the TEelements 704 to the pins 705.

The hot side substrate 702 and the cool side substrate 703 are made froma material and/or constructed with a geometry that results in poorthermal conductivity along the length of the TE element array 701 in thedirection of fluid flow. Preferably, the substrates 702 and 703 are thinso that their relatively poor thermal conductivity does notsignificantly impact the heat transfer from the TE elements 704 to thepins 705. The hot side substrate 702 and the cool side substrate 703hold the TE element array 701 together and have electrically conductiveportions that provide the required conventional electrical connectionsbetween the TE elements 704. Preferably, the material is selectivelyclad with copper or other electrically conductive cladding on both sides(for circuitry and for thermal attachment to the pins 705) with thecopper having a thickness of about 0.050 mm. One preferred material isKapton MT or other flexible, electrically insulative, printed circuitmaterial. For Kapton MT, the thermal conductivity is about 0.5 W/mK andthe thickness about 0.025 mm. Alternatively, the thermal conductivitycould be substantially higher, for example, 20 W/mK, and still have anet positive effect on performance if the substrates 702 and 703 arethin enough (less than about 0.05 mm in one embodiment), or are shapedso as to provide thermal isolation in the direction of flow betweenadjacent pins. The goal of the construction of the TE system 700 is tokeep the individual TE elements 704 substantially thermally isolatedfrom each other in the direction of fluid flow, yet in good thermalcontact with their respective heat exchanger parts.

One particular heat exchanger has been shown above. In order tocapitalize on the efficiency gains available through the presentinvention, it is important that the heat exchangers be efficient at alocal point level. In other words, it is important that at each point ofthe heat exchanger, the medium to be heated or cooled is brought to atemperature that is close to the temperature of the heat exchanger atthat location. Differences in temperature between the medium to becooled as it moves across the thermoelectric system and the heatexchanger at each location decrease the thermal efficiency. Thus, inaccordance with the present invention, the thermoelectric elements aresubstantially thermally isolated in the direction of flow, the heatexchanger is also advantageously thermally coupled to the thermoelectricelements, but substantially thermally isolated in the direction of flow,and the heat exchanger is of a design, taking into account the nature ofthe moving medium, such that at any given location the temperaturedifference between the heat exchanger and the medium to be cooled orheated is small compared to the entire temperature difference from inputto output.

In addition, the level of thermal isolation provided betweenthermoelectric elements depends upon trade-offs and the particularapplication. For example, thermal conduction is desirable to the heatexchanger, but thermal isolation is desirable along the substrate fromthermoelectric element to thermoelectric element. Although betterthermal isolation from element to element may improve efficiency, thatefficiency can be offset by efficiency losses from poor local thermalconduction between the thermoelectric elements and the heat exchanger,or inefficient heat transfer between the heat exchanger and the mediumto be cooled or heated. Therefore, each application requires balancingthese three interrelated properties to achieve a practical, even if notalways optimal, design for the particular application.

One possible construction for the TE system of FIG. 7A is shown in moredetail in FIGS. 7B and 7C. FIG. 7B is an edge view of a portion of theTE system 700 of FIG. 7A. FIG. 7C is a view of the substrates normal tothat of FIG. 7B as seen from the TE side viewed from the bottom of thecold side substrate. FIG. 7C shows one possible layout for the circuittraces for the array of TE elements 704 (for four elements wide). Thenumber of elements along the width or length is chosen to match theapplication, and can be any number. The cold side substrate 703 isshown. The hot side substrate 702 is constructed in the same way in thepresent example. The substrate 703 is shown to be composed of anelectrically insulating layer 714 that provides a structure on which thecircuitry 715 used to connect the TE elements 704 together may becreated. On the opposite side of the electrically insulating layer aremetal pads 716 (FIG. 7B) with which the pins 705 are in good thermalcontact. This contact may be achieved, for instance, by soldering orepoxy bonding. Other methods are also appropriate. The pads 716 need notbe present if the pins are attached directly to the insulating layer 714with good thermal contact and thermal energy transport properties. Thepins can be extensions of the electrically insulating layer so that thepins or other part that serves the function are constructed as a singleunit. Alternately, or in combination, the electrically insulating layercan be anisotropic so that its thermal conductivity is higher in thedirection from a TE element to the pin and lower in the direction offlow. Another way to allow good heat transfer normal to its plane is tomake the insulating layer 714 very thin. Although the insulating layer714 is preferably a good thermal insulator in the direction of flow, thethermal insulation may be provided or further enhanced by gaps 717 inthe insulating layer, thereby replacing the thermal conductivity of theinsulating layer with that of air or another medium between the TEelements 704. The gaps 717 may be filled with highly thermallyinsulative material, in one embodiment.

The TE system 700 of FIG. 7A is configured for fluid flow from right toleft. Fluid 710 at ambient temperature T_(A) enters through suitableducts 711 and is directed past the pins 705 which function as heatexchangers. The fluid exits at the left as cooled fluid 712 at a coolertemperature T_(C) and heated fluid 713 at a higher temperature T_(H). Inthis embodiment, the pins 705, including their heads 706, are not ingood thermal contact with each other so that each pin is effectivelythermally isolated from the others in the direction of fluid flow.Advantageously, the TE element array 701 and particularly the substrates702, 703, are designed to be poor thermal conductors in the direction offluid flow and provide good thermal conductance between the TE elements704 and the pins 705.

The TE elements 704 may be conventional TE elements. However, amodification to the TE elements 704 of the TE element array 701 in thedesign of FIG. 7A can further improve efficiency. In one embodiment, theTE elements 704 are configured to have lower resistance on the right endin FIG. 7A with increasing resistance to the left, or vice versa, butwith the direction of increasing resistance matching the direction offlow. Preferably, the resistance of the last TE element at the higherresistance end is about equal to that of conventional TE elements.Advantageously, the resistance, R, in the x direction (from right toleft in FIG. 7A) is close to $\begin{matrix}{{R(x)} \approx {R_{O}\left( \frac{x}{L} \right)}} & (16)\end{matrix}$

Where

R_(o)=electrical resistance of an element in a conventional TE, and

R(x)=electrical resistance of the TE element at x.

for constant current throughout the TE.

Note that Equation (16) is not followed exactly since R(0) would bezero. Nevertheless, if R(0) is less than ½ R_(o), substantial benefitwill result (assuming the current, I, is constant throughout the TE).Further note at any point other than at the end where fluid exits, theefficiency is higher than that of a conventional device, since bothΔT(x) and R(x) are lower elsewhere, as shown with the followingequations. The efficiency, or COP, at any point x can be approximatedby: $\begin{matrix}{{\beta_{p}(x)} = \frac{{\alpha \quad I\quad T_{c}} - {\frac{1}{2}I\quad {R(x)}} - {K\quad \Delta \quad {T(x)}}}{{\alpha \quad I\quad \Delta \quad {T(x)}} + {I^{2}{R(x)}}}} & (17)\end{matrix}$

where;

R(x)=electrical resistance of the TE element at x  (18)

ΔT(x)=ΔT at x  (19)

β_(p)=COP for this geometry  (20)

The resistance R(x) is less than R_(o) so I²R(x) is smaller than I²R_(o)and ΔT(x) is smaller than ΔT(L). At every point x other than at L, R(x)advantageously is less than R_(o), and ΔT(x) is less than ΔT(L) so thenumerator has its lowest value at L. For the same reason, advantageouslythe denominator is less at x, so β(x) is greater than β(L) for all xless than L. The integral of β(x) from 0 to L is the COP for the device,which by the above is greater than the COP if β effectively wereconstant because of fluid flow patterns or thermal conductivity in thedirection of flow as it is in conventional TE systems. In summary, theTE system of FIG. 7A provides increased efficiency over conventional TEsystems because the average temperature differential between hot side702 and the cold side 703 (ΔT) across the TE system 700 is less thanwith a conventional system, thus increasing its thermodynamicefficiency. This is depicted in the temperature profile graph in FIG.7A. Detailed calculations for COP indicate that β_(P) can be,preferably, 50% to 150% greater than the COP for a comparableconventional device.

One example of a TE system configuration 720 for achieving theincreasing resistance along the length of the device is shown in FIG.7D. In this configuration, once again, a TE element array 721 isconstructed with a hot side substrate 722 and a cool side substrate 723sandwiching a plurality of TE elements 724. A plurality of pins 725 arein good thermal contact with the TE elements 724, via both the hot sidesubstrate 722 and the cool side substrate 723, and form heat exchangersfor the TE system 720. Again, the thermal conductivity along the lengthof the TE element array 721 preferably is minimized, shown by example inFIG. 7C as gaps 726 in the substrates 722 and 723. The flow is from leftto right in FIG. 7C with fluid 727 at ambient temperature T_(A) enteringthrough suitable ducts 728 and flowing past the pins 725 which functionas heat exchangers. The fluid exits at the right as cooled fluid 729 ata temperature T_(C), and heated fluid 730 at a temperature T_(H). Inthis example, the variation in resistance of the TE elements 724 isachieved by a variation in their lengths with the lowest resistance andshortest TE elements 731 advantageously located at the inlet 736 and thehighest resistance and longest TE element 732 located at the outlet end737 of TE system 720. The resistance of the TE elements 724, and hencetheir lengths, are advantageously proportional to ΔT(x) 733 of the twocurves 734 and 735 of the temperature profile shown at the bottom ofFIG. 7C. Note that these two curves 734 and 735 are not straight linesas they were in FIG. 7A. The functional form of the ΔT(x) curve iscontrolled by R(x) and the current and other factors that influenceheating and cooling of the fluid. Whatever the functional form of theΔT(x) curve, the resistance of the elements preferably follow itsgeneral shape.

Yet another example of a TE system 740 in accordance with the presentinvention is shown in FIG. 7E. This embodiment is the same as that shownin FIG. 7D, except that the hot side substrate 742 is a heat exchangerwhich, from the standpoint of the heat produced by the TE system 740 isa heat sink. Preferably, from the standpoint of the heat produced by theTE system 740, the heat sink is essentially infinite. In thisconfiguration, a TE element array 741 is constructed with the hot sidesubstrate 742 and a cool side substrate 743 sandwiching a plurality ofTE elements 744. A plurality of pins 745 are in good thermal contactwith the TE elements 744, via the cool side substrate 743, and form thecool side heat exchanger for the TE system 740. The hot and cold sidesmay be reversed by reversing the electrical current flow direction ifthe application demands heating rather than cooling. Again, the thermalconductivity along the length of the TE element array 741 is minimizedon the cool side substrate 743. As in FIG. 7D, thermal isolation may beenhanced or obtained by gaps 746 in the substrate 743. As in theprevious examples, the gaps 746 may be filled with air or other materialof low thermal conductivity. The flow is from left to right in FIG. 7Ewith fluid 747 at ambient temperature T_(A) entering through a suitableduct 748 and flowing past the pins 745 which function as heatexchangers. The fluid exits at the right as cooled fluid 749 at a coolertemperature T_(C). Variation in resistance of the TE elements 744 isachieved advantageously by a variation in their lengths with the lowestresistance and shortest TE element 751 located at the inlet and thehighest resistance and longest TE element 752 located at the outlet endof TE system 740. The resistance of the TE elements 744, and hence theirlengths in this example, are shown as being substantially proportionalto ΔT(x) 753 of the two curves 754 and 755 of the temperature profileshown at the bottom of FIG. 7C. Curve 755 is a straight line because, inthis example, the hot side substrate 742 is effectively an infinite heatsink. Such a heat sink 742 may be the wall of a vessel wherein the otherside of which is in contact with a large amount of fluid maintained at aconstant temperature by an external means.

Yet another configuration of a TE system 800 that employs thermalisolation of TE elements in accordance with the present invention isshown in FIG. 8. As with FIG. 7A, a TE element array 801 is constructedwith a hot side substrate 702, a cool side substrate 703, a plurality ofTE elements 704, and a plurality of pins 705 in good thermal contactwith the TE elements 704. In this embodiment, thermal isolation in thedirection of flow is employed as before, but a fluid 807 entering viathe cold side duct 808 at ambient temperature T_(A) for flow along thecool side and a fluid 809 entering the hot side duct 810 at ambienttemperature T_(A) for flow along the hot side originate from oppositeends of the TE system 800. The fluids 807, 809 flow across the pins 705to exit at the opposite ends of their respective ducts 808, 810. Theresulting heated fluid 811 exits from one end at temperature T_(H), andthe resulting cooled fluid 812 at temperature T_(C) exits from the otherend, both after flowing across the respective hot or cool sides of theTE system 800.

A particular case of interest is where ΔT(x) and R(x) are constantbecause this tends to be a practical case that balances thermodynamicefficiency considerations, ease of manufacture, and the need to reducewaste side (hot side) flow. If;

ΔT(x)=ΔT_(c)=ΔT_(h)=ΔT  (21)

then approximately; $\begin{matrix}{\beta_{c} = \frac{{\alpha \quad I\quad T_{c}} - {\frac{1}{2}I^{2}R} - {K\quad \Delta \quad T}}{{\alpha \quad I\quad \Delta \quad T} + {I^{2}R}}} & (22)\end{matrix}$

β_(c)=COP for this geometry  (23)

If this approximate result is compared with the related equation for COPfor a conventional device with ΔT_(h)=ΔT_(c), then the present systemwill be more efficient, since in (23) ΔT=ΔT_(c), while in a conventionaldevice,

ΔT=ΔT _(c) +ΔT _(h)  (24)

and for the assumption that ΔT_(c)=ΔT_(h)

ΔT=2ΔT_(c)  (25)

Thus from (22) β_(c) will be greater than β (Equation 14), as anexample, for the following design parameters;

α=10⁻¹ V/K

I=3 A

R=2 Ω

K=2 W/mK

T_(c)=280 C

ΔT_(c)=ΔT_(h)=10 C

Equation (22) yields;

β_(c)=2.11  (26)

and for the conventional design with ΔT=2ΔT_(c);

β=1.40  (27)

Further, the fraction of the total flow on the waste side 809, 811 isreduced since the efficiency of the system is greater, and so relativelyless heat from q_(in) is rejected from the waste side 809, 811, in thepresent design.

The temperature profile for the fluid for the TE system 800 of FIG. 8Ais illustrated in the lower portion of the figure.

All of the above geometries provide variations of the invention relatingto isolating TE elements thermally in the direction of fluid flow. Thebenefits of the isolated element geometries disclosed above include:

(1) The thermodynamic efficiency can be substantially higher;

(2) The fluid flow fraction on the main side (the side of interest inthe particular application, cool or hot) can be substantially greater.

Although particular embodiments are disclosed above, any configurationwhich causes or provides the thermal isolation efficiencies explainedabove are within the scope of the invention. In addition, enhancementssuch as decreased resistance are added improvements, on top of theisolation efficiencies obtained through the embodiments disclosed above.

FIGS. 7A-E and FIG. 8 have illustrated the important feature of thermalisolation of TE elements in the direction of flow along with theenhancement of performance due to the increase in resistance of theelements in the direction of flow. FIGS. 9A through 9E show otherexamples of embodiments incorporating these features but utilizingdifferent geometries for the heat exchangers and the TE elements.

FIGS. 9A and 9B show such an embodiment of a TE system 900 in which theheat exchanger has fins rather than pins. FIG. 9A is a side view andFIG. 9B is an end view. As illustrated, a TE element array 901 isconstructed with a hot side substrate 902 and a cool side substrate 903sandwiching a plurality of TE elements 904. A plurality of heatexchangers 905 are in good thermal contact with the TE elements 904, viaboth the hot side substrate 902 and the cool side substrate 903.Electrical connection from element to element is made via circuitry 908preferably bonded to the substrates 902 and 903 and to the TE elements904. As shown, the heat exchangers 905 consist of a corrugation of thinmetal fins 906 which are in good thermal contact with the TE elements904 (hot and cold side) through the substrates 902 and 903. Preferably,the heat exchangers 905 are constructed of copper or other materialhaving high thermal conductivity and having as flat a bottom edge 907 aspossible to provide maximum surface area in contact with the substrates902 and 903. The thermal conductivity in the direction of flow (normalto the plane of FIG. 9B) is minimized in this embodiment by havingseparate heat exchangers 905 for each row of TE elements 904 separatedby gaps 909.

Shown in FIG. 9C is another embodiment of a TE system 920 depicting theuse of heat pipes 925 and a heat sink 926. A TE element array 921 isconstructed with a hot side substrate 922 and a cool side substrate 923sandwiching a plurality of TE elements 924. In this configuration, theTE system is configured for cooling. Once again, the cold side substrate923 has poor thermal conductivity in the direction of flow. A pluralityof heat pipes 925 are in good thermal contact with the TE elements 924via the cool side substrate 923, and transfer heat between the cool sidesubstrate 923 and the heat exchangers 926 shown as an example, at theends of the heat pipes 925. In this embodiment, the direction of flow isfrom bottom to top in FIG. 9C. In the TE system 920 depicted in FIG. 9C,the hot side substrate 922 is in good thermal contact with a heat sink926. Advantageously, from the standpoint of the heat produced by the TEsystem 920, the heat sink 926 is effectively infinite. The TE system 920as shown can also employ the change in resistance of the TE elements 924along the direction of flow. The lowest resistance element 927 is at theflow inlet side 929 and the highest resistance element 928 is at theflow outlet side 930. The resistance in this case is inverselyproportional to the cross-sectional area of the TE elements 924 with thedecrease in cross-sectional area proceeding from the inlet 929 to theoutlet 930 thereby causing the resistance to increase in the oppositedirection. The TE elements 924 are electrically connected with circuitryas described above, but not shown in this figure for clarity.

Yet another example of an isolated element TE system 940 for cooling isshown in FIGS. 9D and 9E. FIG. 9D is an end view and FIG. 9E is a sideview. The construction depicted shows one preferred way to make a finnedheat exchanger 945. As shown, the TE element array 941 is constructedwith a hot side substrate 942 and a cold side substrate 943. At leastthe cold side substrate 943 has low thermal conductivity in thedirection of flow. These substrates 942 and 943 sandwich a plurality ofTE elements 944 electrically connected together with circuitry 949 asdescribed above. A single fin array 945 is in good thermal contact withthe TE elements 944 via the cold side substrate 943. Despite being asingle piece, thermal conductivity in the direction of flow through thefin array 945 is reduced by the gaps 946 between adjacent fin sections.Tabs 947 hold the entire array together. Advantageously, these tabs 947are small enough in comparison to the gaps 946, that they do notsignificantly increase heat transfer between adjacent fin sections. Theenhancement that can be obtained through TE element resistance change isdepicted with increasing lengths of the TE elements 944 as flow proceedsfrom the inlet 950 to the outlet 951 in FIG. 9E. As with previousembodiments, the varying resistance could be obtained in other ways,such as varying the cross-section of the TE elements 944, varying the TEelement material resistivity, or combinations of varying the length,cross-section, and resistivity of the TE elements. Finally, a heat sink948 is in good thermal contact with the hot side substrate 942. Thisheat sink is preferably of the type described in FIGS. 7E and 9C.

FIG. 10 shows a another embodiment that achieves a performanceenhancement similar to that previously described due to a change in theresistance (and isolated elements) of the TE elements in the directionof flow. In this embodiment, the resistances of the TE elements are thesame throughout the device but the voltages applied to the elements arevaried along the direction of flow.

In FIG. 10, an example of a TE system 1000 is shown in which a TEelement array 1001 is constructed with a hot side substrate 1002 and acool side substrate 1003 sandwiching a plurality of TE elements 1004. Aplurality of heat exchangers 1005 are in good thermal contact with theTE elements 1004, via both the hot side substrate 1002 and the cool sidesubstrate 1003. The heat exchangers 1005 and the substrates 1002, 1003can have any of the configurations depicted in the previous embodiments.The heat exchangers 1005, like those described in FIGS. 9A and 9B, arein good thermal contact with TE elements 1004 (hot side 1011 and coldside 1010) through the substrates 1002 and 1003. As shown in FIG. 10,the flow on both the hot side 1011 and the cold side 1010 is from leftto right. Fluid 1009 enters at the left at ambient temperature T_(A) andpasses over or through the heat exchangers 1008 gradually changing intemperature throughout the length of the TE system 1000 until it exitsat the right as fluid 1010 at a reduced temperature T_(C) on the coldside and as fluid 1011 at a raised temperature T_(H) on the hot side.Electrical connection from TE element to TE element is made via thecircuitry 1008 connected to the substrates 1002 and 1003 and to the TEelements 1004. Rather than the interconnection circuitry on thesubstrates as in the previous embodiments, the substrate circuitry 1008does not connect all the TE elements 1004 in series.

In FIG. 10, the circuitry 1008 is constructed so that individual TEelements 1004 or rows of TE elements 1004 normal to the direction offlow can have differing sources of voltage and therefore can havedifferent currents running through the elements or rows. Accordingly, asdepicted in FIG. 10, various control voltages 1020 can be provided forvarious segments or sections of the thermoelectric array 1001. In oneembodiment, a plurality of sensors 1013, 1014, 1015 are coupled to acontrol system 1012 are provided to monitor the TE system. The controlsystem 1012 is coupled to the plurality of control voltages 1020 tocontrol the currents provided to the different elements or rows in theTE array 1001. The voltages along the length of the TE system 1000 maybe varied via the control system 1012 depending upon external conditionsor upon conditions within the system itself. These conditions, some orall of which may be present, include external temperature or flow,internal temperature or flow, and user selectable inputs to manuallycontrol the desired amount of heating or cooling by particular TEelements or rows of TE elements.

The conditions, such as external temperature or flow, internaltemperature or flow, can be monitored through sensors such as thesensors 1013, 1014. The user selectable inputs can be provided throughknobs, dials, push buttons, or other programmable means of the controlsystem 1012. For example, a user interface 1015 can be provided for theuser selectable or configurable inputs. Advantageously, through the userinterface 1015, the conditions monitored or the trip levels for theconditions monitored via the sensors 1013 and 1014 can be modified tocustomize the TE system for its particular application or the particularcondition to which it is subjected at any given time. The sensors 1013,1014, and 1015 are monitored by control circuitry 1012 which, using hardwired or software relationships (whose nature depends upon theapplication), causes the voltages applied to vary in accordance with thesensor inputs.

An advantage of this type of system is that it permits the thermal powergenerated by the TE elements 1004 to be varied as desired to achieveimprovement in efficiency. For example, this allows adjustments to thecurrent through the TE elements 1004 as flow conditions change from timeto time. The ability through this embodiment to obtain efficiency gainscan be understood with Equation 32 which gives the current for optimumefficiency I_(opt)(x) for the TE system at any point x along it length.$\begin{matrix}{{I_{opt}(x)} = \frac{{\alpha\Delta}\quad {T(x)}}{R\left( {\sqrt{1 + {Z\quad T}} - 1} \right)}} & (28)\end{matrix}$

In Equation (28) the parameters α and Z are properties of the TEmaterial. R is the resistance of the TE elements 1004 and for discussionof the embodiment of FIG. 10 can be considered constant throughout theTE system 1000. Therefore Equation (28) shows that for optimumefficiency, I_(opt) is proportional to ΔT. To achieve I_(opt), it isnecessary to make the voltage across elements at position x to be theproduct of I_(opt)(x) an R. Since in the example ΔT increases from zeroat the left to its maximum value at the right, the leftmost elementsshould be powered with as low a voltage as practical, and increase to amaximum value at the exit 1010 and 1011. Thus in FIG. 10, 0≈V₁<V₂<V₃ . .. <V_(n). Advantageously, the variation of voltage with position x alongthe direction of flow should approximate; $\begin{matrix}{{V(x)} = \frac{{\alpha\Delta}\quad {T(x)}}{\left( {\sqrt{1 + {Z\quad T}} - 1} \right)}} & (29)\end{matrix}$

FIG. 11 presents yet another example of a TE system 1100 in accordancewith one aspect of the present invention in which the performanceenhancement due to resistance change is achieved by mechanical means. ATE element array 1101 is constructed with a hot side substrate 1102 anda cold side substrate 1103 sandwiching a plurality of TE elements 1104.In this embodiment, the TE elements 1104 are made from a liquid TEmaterial 1109 contained within tubes 1110 whose ends are closed by acombination of interconnection circuitry 1108 and hot and cold sidesubstrates 1102 and 1103. One possible example of liquid TE materialsare mixtures of Thallium and Tellurium (p-type) at temperatures (aboveroom temperature) where it becomes liquid, and a mixture ofmercury/rubidium (n-type). Another example P-type Bismuth and Telluridesluried in mercury and N-type bismuth and telluride sluried in mercury.Some such materials are described by A. F. Loffe, in SemiconductorThermal Elements, and Thermoelectric Cooling, Infosearch, London, 1957.

A plurality of heat exchangers 1105 are in good thermal contact with theTE elements 1104, via the cold side substrate 1103. As shown in thisexample, the heat exchangers 1105 are like those described in FIGS. 9Aand 9B and are in good thermal contact with TE elements 1104 via thecold side substrate 1103. As described above, the heat exchangers may beof a number of different types, such as the nail, fins, or heat pipes,or any of a number of other heat exchanger types. As before, the TEelements 1104 are substantially or at least significantly thermallyisolated in the direction of fluid flow on the cold side 1103. A heatsink 1114 (from the standpoint of the TE system 1100 being effectivelyinfinite) is in good thermal contact with the TE elements 1104 via thehot side substrate 1102. In this embodiment, a piston 1107 is providedfor at least some of and possibly all of the TE elements 1104. Thepistons have holes 1108 and are coupled to actuators 1115 which arecoupled to a system controller 1116. The system controller 1116 iscoupled to a plurality of sensors 1117, 1118 and 1119. For example, thesensors may be external sensors 1117, internal sensors 1118, and usercontrolled or user input devices 1119. Advantageously, the systemcontroller 1116 provides hardware or microprocessor-based computercontrol for the actuators 1115 and includes power source or drivers forthe actuators 1115 to provide sufficient current required by theactuators 1115. Electrical connection from TE element to TE element ismade via circuitry 1106 connected to the substrates 1102 and 1103 and isin contact with a surface of TE elements 1104 and also with the pistons1107. Electrical contact from the pistons 1107 to the hot side substrate1102 is achieved with sliding contacts 1113. The holes 1108 in thepistons 1107 allow the liquid TE material 1109 to pass through the holes1108 as the pistons move. At any position, the pistons 1107 divide theliquid TE material into forward sections 1111 and aft sections 1112. Inthis embodiment, the pistons 1107 are made from an electricallyconductive material whose conductivity is substantially greater thanthat of the liquid TE material 1109. When the pistons 1107 are not fullyagainst the hot side circuitry 1106 so that aft section 1112 is not ofzero volume, a portion of the liquid TE material 1109 is effectivelyshorted by the pistons 1107, thereby reducing the resistance of the TEelements 1104 to some value less than their maximum resistances. Thus,the position of the pistons 1107 is adjustable to vary the resistancesof the TE elements 1104 along the length of the TE system 1100 inaccordance with a fixed or time-varying scheme. The control scheme canbe similar to that described for FIG. 10, except that advantageously,instead of varying the voltages applied to the TE elements 1104, theposition of the pistons 1107 is varied by use of the actuators 1115controlled by the controller 1116 or other power source in response tochanges in inputs from external sensors 1117, internal sensors 1118,user input sensors 1119, or other signaling devices.

As understood in the art, the performance of certain TE materials may beenhanced by the application of suitable magnetic fields. FIG. 12 showsan embodiment of a TE system 1200 in which the material structure of TEelements 1204 is such that a magnetic field is generally applied acrossthe width of the TE elements. As shown, a TE element array 1201 isconstructed with a hot side substrate 1202 and a cold side substrate1203 sandwiching a plurality of TE elements 1204. Heat exchangers 1205are in good thermal contact with the TE elements 1204 via the hot andcold side substrates 1202 and 1203. As shown, the heat exchangers 1105are of any suitable configurations such as those described in FIGS. 9Aand 9B. In this embodiment, substantial or significant thermal isolationof the TE elements 1204 in the direction of flow is employed as before.Series electrical connection of the TE elements is achieved by circuitry1206 bonded or otherwise fixed to the hot and cold side substrates 1202and 1203 and to the TE elements 1204. For example for some TE materials,a suitable magnetic field can be applied from permanent magnets 1207 alloriented in the same direction with respect to their polarity (shown byN for north and S for south in FIG. 12). The magnetic field 1208 (shownby the dashed lines) therefore passes through the widths of the TEelements 1204.

FIG. 13 shows an embodiment of a TE system 1300 in which the materialstructure of TE elements 1304 is such that enhancement is achieved bythe application of a suitable magnetic field across the length of the TEelements. As shown, a TE element array 1301 is constructed with a hotside substrate 1302 and a cold side substrate 1303 sandwiching aplurality of TE elements 1304. In this embodiment, heat exchangers 1305are in good thermal contact with permanent magnets 1307 which are, inturn, in good thermal contact with the TE elements 1304 via cold sidesubstrate 1303. In one embodiment, the magnets form the heat exchangers.Alternatively, the heat exchangers 1305 are similar to those describedin FIGS. 9A and 9B. In this embodiment, substantial or significantthermal isolation of the TE elements 1304 in the direction of flow isemployed. A heat sink 1309 (from the standpoint of the TE system 1300being substantially infinite) is in good thermal contact with the TEelements 1304 via the hot side substrate 1302. The heat sink 1309 can bemade from a material with high magnetic permeability such as iron.Series electrical connection of the TE elements 1304 is achieved bycircuitry 1306 bonded or otherwise attached to the hot and cold sidesubstrates 1302 and 1303 and to the TE elements 1304. The magnetic fieldis applied from the permanent magnets 1307 directionally oriented inpairs with respect to their polarity (shown by N for north and S forsouth in FIG. 13). The magnetic circuit is completed on the hot sidethrough the high magnetically permeable heat sink 1309. The magneticfield 1308 (shown by the dashed lines) therefore substantially passesthrough the lengths of the TE elements 1304.

In the embodiments disclosed above, the media to which heat istransferred or from which it is extracted has been a fluid. FIG. 14depicts a construction in which the fluid is replaced by a solid. A TEsystem 1400 is shown with a TE element array 1401 constructed with a hotside substrate 1402 and a cold side substrate 1403 sandwiching aplurality of TE elements 1404. A heat sink 1409 (from the standpoint ofthe TE system 1400 being substantially infinite) is in good thermalcontact with the TE elements 1404 via the hot side substrate 1402.Series electrical connection of the TE elements 1404 is achieved bycircuitry 1407 bonded or otherwise attached to the hot and cold sidesubstrates 1402 and 1403 and to the TE elements 1404. Solid material1405 (in the case shown) to be cooled moves from left to right in thefigure and is in good thermal contact with the TE elements 1404 via thecool side substrate 1403. Good thermal conductivity at the interfacebetween the solid 1405 and the cool side substrate 1403 can be achievedfor example by thermal grease 1406. As the solid 1405 passes along thecool side substrate 1403 it is cooled progressively by the TE elements1404. Advantageously, the solid material has good thermal conductivityfrom the TE elements 1404 through the substrate 1403 and grease 1406 andthrough the solid 1405 but not along the solid in the direction ofmotion. Suitable materials for the solid 1405 can be composites or otherthermally anisotropic materials, or the solid 1405 can be slottedperpendicular to the direction of motion and the slots filled with athermal insulator, as examples.

FIGS. 15A through 15G show examples of various temperature profilesalong the length of an isolated element TE system. In all of thesefigures, hot side flow is depicted as from right to left and cold sideflow is from left to right. For those cases in which one side has a heatsink, there is no flow on the side with the heat sink. Point O is alwaysat the left representing the entry end for cold side flow and the exitend for hot side flow. Point L is always at the right representing theexit end for cold side flow and the entry end for hot side flow. Thehorizontal line always represents ambient temperature, T_(A). FIG. 15Adepicts the case in which ΔT_(C)=ΔT_(H). FIG. 15B depicts the case inwhich ΔT_(C)>ΔT_(H). FIG. 15C depicts the case in which ΔT_(C)<ΔT_(H).FIG. 15D depicts the case in which the hot side has an infinite heatsink and therefore ΔT_(H)=0. FIG. 15E depicts the case in which the coldside has an infinite heat sink and therefore ΔT_(C)=0. FIG. 15F depictsthe case in which cold fluid enters at a temperature T_(CIN)<T_(A). FIG.15G depicts the case in which hot fluid enters at a temperatureT_(HIN)>T_(A). Other temperature profiles can be envisioned and devicesconstructed to produce all possible combinations of heat sinks, inputtemperatures and output temperatures in accordance with the teachings ofthe present invention.

In the dual mode operation, the idealized equation (9) illustrates thatwhen the COP in cooling mode is optimized, so is the COP in heatingmode; however, the flow rates, the variation in TE element resistancevs. position, or the variation in TE element current vs. position, mayno longer be appropriate for the application. The adjustment of theseparameters as guided by the fundamental equations of thermoelectrics canbe made to optimize overall system performance.

FIG. 16 shows another embodiment of a TE system 1600 in which flow onthe waste side traverses the length of the TE array 1601 in sections1609. As with the previous embodiments, the TE array 1601 is constructedwith a hot side substrate 1602 and a cool side substrate 1603sandwiching a plurality of TE elements 1604. A plurality of pins 1605are in good thermal contact with the TE elements 1604, via both the hotside substrate 1602 and the cool side substrate 1603, and form heatexchangers for the TE system 1600. As shown, the pins 1605 have a formvery similar to nails, with their heads 1606 in good thermal contactwith the TE elements 1604 (hot and cold side). Preferably, the pins 1605are constructed of copper or other material having high thermalconductivity. Depending upon the application or the fluids to which heattransfer takes place, the pins 1605 may be replaced with other heatexchanger configurations or geometries some of which have been describedabove.

The hot side substrate 1602 and the cool side substrate 1603 along withthe circuitry 1606 are constructed as described for FIGS. 7A through 7Cmaintaining the property of thermal isolation of the TE elements 1604along the length of the TE array 1601. A hot side duct 1607 is attachedto the hot side of the TE system 1600 to direct fluid entering at theleft at temperature T_(A) past the heat exchangers 1605 on the hot side,and exiting at the right at temperature T_(H). A plurality of ducts 1608are attached to the cold side of the TE system 1600 to direct fluid pasta plurality of sections 1609 of heat exchangers 1605. Fluid attemperature T_(A) enters the leftmost two ducts 1608 at their respectiveleft ends and exits at their respective right ends. Fluid at temperatureT_(A) enters the rightmost duct 1608 at its right end and exits at itsleft end. The figure shows three sections 1609 in the cool side which isthe waste side in the depicted embodiment, but there can be any numberand they do not all have to be the same length or flow in the samedirection. The cool side exit temperatures, T_(C1), T_(C2), etc. do nothave to be the same nor does the amount of fluid passing through each.

Because cool side air is introduced at T_(A) at a plurality of pointsalong the length of TE system 1600, ΔT across the TE elements 1604 canbe smaller than it would be if the cool side air passed by all of theheat exchangers 1605 on the cool side prior to being exhausted. As shownin Equation 10, the COP is made larger when ΔT is smaller; therefore thehot side of TE system 1600 can be made even warmer than it would be witha single cool side duct. This is depicted in the temperature profilegraph at the bottom of FIG. 16. At each point of introduction of fluidat temperature T_(A) (the points 0, L₁, L₂ . . . ) the COP of theprevious section has become relatively smaller. The new fluid at T_(A)raises the COP of the stage into which it is introduced, therebyachieving additional ΔT throughout that section. Note that generally,the net ΔT added by each section will diminish down the length of thedevice unless the fluid introduced at the later stages (L₂ etc.) is at atemperature higher than T_(A), or the heat sinking ability in the laterstages is sufficiently large.

The embodiment shown in FIG. 16 showed the TE system operating inheating mode. This same technique can be used to augment the performanceof a TE system similarly constructed in cooling mode, wherein the fluidon the waste side enters at more than one point.

FIG. 17 shows another embodiment of a TE system 1700 in which flow onthe waste side (cooling side) traverses the length of the TE array 1701in sections 1709. FIG. 17 differs from FIG. 16 in that in FIG. 17, theflow is from opposite ends of the TE system 1700. The TE array 1701 isconstructed with a hot side substrate 1702, cool side substrate 1703, aplurality of pin 1705, circuitry 1706, hot side duct 1707 and pluralityof duct 1708 for a plurality of section 1709 of heat exchangers 1705,just as in FIG. 16.

Again, the embodiment shown in FIG. 17 depicts the TE system operatingin heating mode. This same technique can be used to augment theperformance of a TE system similarly constructed in cooling mode,wherein the fluid on the waste side enters at more than one point.Furthermore, not all of the waste side fluid need flow in the samedirection, enter at the same temperature, flow in equally spaced orequal length section, or have the same fluid flow rate.

FIG. 18 shows another embodiment of a TE system 1800 in which flow onthe waste side may not traverse the entire length of the TE array 1801.The TE array 1801 is constructed with a hot side substrate 1802, a coolside substrate 1803, and a plurality of pins 1805 just as in FIG. 16. Ahot side duct 1807 is attached to the hot side of the TE system 1800 todirect fluid entering at the left at temperature T_(A) past the heatexchangers 1805 on the hot side, and exiting at the right at temperatureT_(H). A duct 1808 is attached to the cold side of the TE system 1800 todirect fluid past the heat exchangers 1805. Fluid enters the cool sideduct 1808 at temperature T_(A) at the left end in the figure. A valve1809 has two positions, one (open) allowing fluid to flow through theentire duct 1808 so that it exits at the right end 1811 at temperatureT_(C). The other position (closed) of the valve 1809 allows the fluid toflow through only a portion of the duct 1808 so that it exits at anintermediate position 1810 at temperature T_(C)*. The figure shows twosections 1812, but there can be any number and they are not necessarilythe same length, have fluid flow in the same direction, or have fluidentering at the same temperature.

If the valve 1809 is in its open position and the TE system 1800 isrequired to produce only a small ΔT, the temperature profiles are 1820and 1821 (long dashes) as shown at the bottom of FIG. 18. Note that atthe exit point L₂ the slope of the cool side curve is non-zero andtherefore the heat flow is non-zero. Thus in this situation, the TEsystem 1800 is still removing heat from the cool side and is stilldelivering heat to the hot side. If, with the valve still in its openposition, the TE system 1800 is required to produce a large ΔT, morepower to the TE elements 1804 is necessary for sufficient ΔT, and thecool side temperature profile could approximately follow the curves 1822and 1823. Note that at some intermediate point L₁, the slope of the coolside temperature is effectively zero. If flow is allowed to continuepast L₁, the cool side temperature would continue along the curve (shortdash) 1823. If the valve 1809 is closed, thereby dumping the fluid outthe exit point 1810, effectively all of the joule heating except forthermal losses is available to further increase the hot side temperatureto T_(H)*, following the hot side temperature profile 1824.

The technique of removing the flow from a portion of the TE array 1801may also be employed with the device configured with flow from oppositeends. Further, the valve 1809 and the single cool side duct 1808 may bereplaced by a plurality of valves and ducts.

In all of the embodiments described above, there may be a systemcontroller similar to that described for FIGS. 10 and 11. Thosedescriptions focused on the use of the controller to adjust voltages onTE elements (FIG. 10) and to adjust the position of pistons (FIG. 11).The controller may also use the information from the same or similarsensory inputs along with its hard wired or software relationships toadjust, for example, the current (for series connection of TE elements)or the hot side or cold side flow rates. The relationships may be in theform of look-up tables, formulas, or other algorithmic processes. Theuse of such a controller therefore offers the opportunity to improveoverall efficiency to reduce average input power, or to otherwise changesystem output.

The controller depicted contemplates the possibility of monitoringseveral parameters, and dynamically adjusting the system in response tothese parameters. However, the control system may be a very simplesystem, such as a switch, controlled by a user. For example, the controlsystem may be no more than a switch that reverses current in thethermoelectric system to change from cooling to heating, or alters thecurrent to dynamically adjust the amount of current to thereby cause achange in the amount of cooling or heating, with the sensory input beinga person who decides the temperature is too hot or too cold.

The above descriptions suggest that each row of TE elements would varyin length, area, resistivity or in power applied. For manufacturability,simplicity, and cost, groups of TE elements could be the same, orconstructed as submodules. Thus, not every row need be different. Suchsimplification would still increase efficiency, with the improvementdependent on how many different sizes, power, levels, etc. would beused.

In the above embodiments, in which a heat sink can be employed, the heatsink can be replaced by a heat pipe or other heat transport mechanism.Thus, the heat sink, or the like could be located remotely, or theassembly could be linked to one or more other assemblies that wouldextract waste thermal power. In addition, although fluids and solidshave been depicted for the medium to be cooled or heated, a combinationof fluid and solid, such as a slury, could also be the medium to becooled or heated. Finally, the various ways of improving efficiency havebeen described in combination with the thermal isolation feature.However, the enhancements to efficiency, such as changing resistance,varying current, and others described above may be used together oralone, as appropriate in the particular application.

The embodiments described above have focused the discussion on the coolside or cooling feature of the TE systems presented. By reversing thedirection of current flowing through such devices or reversing theoutput from hot side to cold side, heating, or heating and cooling canalso be provided with the same or similar configurations. Optimizationfor any particular usage will depend upon the specific application forthe TE system. Nevertheless, a few potential differences may occur in aparticular application:

1) In the heating mode, in automotive, home, and industrial heatingsystems, for example, the required ΔT_(H) could be substantially higherthan ΔT_(C);

2) the mass flow ratio (main side to waste side) may require adjustmentto optimize performance;

3) the capability of today's TE thermal pumping power limits ΔT acrossthe device to about 70° C., so to achieve high ΔT_(H) with high COP,configurations and flow patterns may need to be adjusted as required byany particular application; and

4) when the system is required to operate in either heating or coolingmode on demand, (HVAC or heat pump systems) the design advantageouslywould be sufficiently flexible to operate efficiently in both modes.

What is claimed is:
 1. A thermoelectric system for use with at least onemedium to be cooled or heated, comprising: a plurality of thermoelectricelements forming a thermoelectric array with a cooling side and aheating side, wherein the plurality of thermoelectric elements aresubstantially thermally isolated from each other in at least onedirection across the array; and at least one heat exchanger on at leastthe cooling and/or the heating side in thermal communication with atleast one thermoelectric element, the heat exchanger configured tosignificantly maintain the thermal isolation of the thermoelectricelements.
 2. The thermoelectric system of claim 1, wherein the at leastone medium moves across at least a portion of at least one side of thearray, in at least one direction.
 3. The thermoelectric system of claim2, wherein at least one characteristic of some of the thermoelectricelements is varied in the direction of medium movement.
 4. Thethermoelectric system of claim 3, wherein the at least onecharacteristic comprises at least the resistance of at least some of thethermoelectric elements.
 5. The thermoelectric system of claim 4,wherein the resistance is varied through variation of length of at leastsome of the thermoelectric elements.
 6. The thermoelectric system ofclaim 4, wherein the resistance is varied through variation ofcross-sectional area of at least some of the thermoelectric elements. 7.The thermoelectric system of claim 4, wherein the resistance is variedthrough mechanical configuration of at least some of the thermoelectricelements.
 8. The thermoelectric system of claim 4, wherein theresistance is varied through resistivity of at least one thermoelectricmaterial.
 9. The thermoelectric system of claim 1, wherein the currentthrough the thermoelectric elements is different for at least somethermoelectric elements in the array.
 10. The thermoelectric system ofclaim 2, wherein the heat exchanger comprises a plurality of portions,at least some of the portions in thermal communication with at least onethermoelectric element, at least some of the portions substantiallythermally isolated from other of said portions in the direction ofmedium movement.
 11. The thermoelectric system of claim 10, wherein atleast some of the portions comprise posts.
 12. The thermoelectric systemof claim 10, wherein at least some of the portions comprise heat pipes.13. The thermoelectric system of claim 10, wherein at least some of theportions comprise fins.
 14. The thermoelectric system of claim 1,wherein at least one heat exchanger is on each of the cooling and theheating sides.
 15. The thermoelectric system of claim 1, wherein oneside has a heat sink and one side has the at least one heat exchanger.16. The thermoelectric system of claim 15, wherein the heat sink isprovided by at least one heat pipe on one end in thermal communicationwith one side of the thermoelectric array and on the other end inthermal communication with a heat sink.
 17. The thermoelectric system ofclaim 1, wherein the thermoelectric elements are subjected to at leastone magnetic field.
 18. The thermoelectric system of claim 1, whereinthe medium comprises at least one fluid.
 19. The thermoelectric systemof claim 1, wherein the medium comprises at least one solid.
 20. Thethermoelectric system of claim 1, wherein the medium comprises acombination of at least one fluid and at least one solid.
 21. Thethermoelectric system of claim 3, wherein the at least onecharacteristic is dynamically adjustable through adjustment of themechanical configuration of the thermoelectric system.
 22. Thethermoelectric system of claim 21, wherein a control system coupled tosaid thermoelectric system adjusts the mechanical configuration basedupon at least one input to the control system.
 23. The thermoelectricsystem of claim 22, wherein the control system operates according to atleast one algorithm.
 24. The thermoelectric system of claim 3, wherein acontrol system coupled to said thermoelectric system adjusts the atleast one characteristic based upon at least one input to the controlsystem.
 25. The thermoelectric system of claim 24, wherein the controlsystem operates according to at least one algorithm.
 26. Athermoelectric system for use with a directional movement of at leastone medium to be cooled or heated, comprising: a plurality ofthermoelectric elements forming a thermoelectric array with a coolingside and a heating side, wherein at least one characteristic of at leastsome of the thermoelectric elements is varied in the direction of mediummovement.
 27. The thermoelectric system of claim 26, wherein the atleast one characteristic comprises at least the resistance of at leastsome of the thermoelectric elements.
 28. The thermoelectric system ofclaim 27, wherein the resistance is varied through variation of lengthof at least some of the thermoelectric elements.
 29. The thermoelectricsystem of claim 27, wherein the resistance is varied through variationof cross-sectional area of at least some of the thermoelectric elements.30. The thermoelectric system of claim 27, wherein the resistance isvaried through mechanical configuration of at least some of thethermoelectric elements.
 31. The thermoelectric system of claim 27,wherein the resistance is varied through resistivity of at least onethermoelectric material.
 32. The thermoelectric system of claim 26,wherein the at least one characteristic is dynamically adjustablethrough adjustment of the mechanical configuration of the thermoelectricsystem.
 33. The thermoelectric system of claim 32, wherein a controlsystem coupled to said thermoelectric system adjusts the mechanicalconfiguration based upon at least one input to the control system. 34.The thermoelectric system of claim 33, wherein the control systemoperates in accordance with at least one algorithm.
 35. Thethermoelectric system of claim 26, wherein the at least onecharacteristic comprises at least the current through the thermoelectricelements.
 36. The thermoelectric system of claim 26, wherein thethermoelectric array has at least one heat exchanger on at least thecooling side or the heating side.
 37. The thermoelectric system of claim36, wherein the heat exchanger comprises a plurality of portions, atleast some of the portions in thermal communication with at least onethermoelectric element, at least some of the portions substantiallythermally isolated from other of said portions in the direction ofmedium movement.
 38. The thermoelectric system of claim 37, wherein atleast some of the portions comprise posts.
 39. The thermoelectric systemof claim 37, wherein at least some of the portions comprise heat pipes.40. The thermoelectric system of claim 37, wherein at least some of theportions comprise fins.
 41. The thermoelectric system of claim 36,wherein at least one heat exchanger is on each of the cooling side andthe heating side.
 42. The thermoelectric system of claim 36, wherein oneside has a heat sink and the other side has a heat exchanger.
 43. Thethermoelectric system of claim 26, wherein the thermoelectric elementsare subjected to at least one magnetic field.
 44. The thermoelectricsystem of claim 26, wherein the medium comprises at least one fluid. 45.The thermoelectric system of claim 26, wherein the medium comprises atleast one solid.
 46. The thermoelectric system of claim 26, wherein theat least one medium comprises a combination of at least one fluid and atleast one solid.
 47. The thermoelectric system of claim 26, wherein acontrol system coupled to said thermoelectric system adjusts the atleast one characteristic based upon at least one input to the controlsystem.
 48. The thermoelectric system of claim 47, wherein the controlsystem operates in accordance with at least one algorithm.
 49. A methodof making an improved thermoelectric system for use with at least onemedium to be cooled or heated, comprising the steps of: forming aplurality of thermoelectric elements into a thermoelectric array with acooling side and a heating side; wherein the plurality of thermoelectricelements are substantially thermally isolated from each other in atleast one direction across the array; and exchanging heat from at leastone side of the thermoelectric array in a manner that significantlymaintains the thermal isolation of the thermoelectric elements.
 50. Themethod of claim 49, further comprising the step of moving the at leastone medium across at least a portion of at least one side of the arrayin at least one direction.
 51. The method of claim 50, furthercomprising the step of varying at least one characteristic of thethermoelectric elements in the direction of medium movement.
 52. Themethod of claim 51, wherein the step of varying comprises varying atleast the resistance of at least some of the thermoelectric elements.53. The method of claim 52, wherein the step of varying the resistancecomprises varying the length of at least some of the thermoelectricelements.
 54. The method of claim 52, wherein the step of varying theresistance of the thermoelectric elements comprises varyingcross-sectional area of at least some of the thermoelectric elements.55. The method of claim 52, wherein the step of varying the resistanceof the thermoelectric elements comprises varying the mechanicalconfiguration of at least some of the thermoelectric elements.
 56. Themethod of claim 52, wherein the step of varying the resistance of thethermoelectric elements comprises varying resistivity of at least someof the thermoelectric elements.
 57. The method of claim 49, furthercomprising the step of varying the current through at least somethermoelectric elements in the array.
 58. The method of claim 50,wherein the step of exchanging heat comprises providing a heat exchangercomprising a plurality of portions, each portion in thermalcommunication with at least one thermoelectric element, at least some ofthe portions substantially thermally isolated from other portions in thedirection of medium movement.
 59. The method of claim 58, wherein atleast some of the portions comprise posts.
 60. The method of claim 58,wherein at least some of the portions comprise heat pipes.
 61. Themethod of claim 58, wherein at least some of the portions comprise fins.62. The method of claim 49, wherein the step of exchanging heatcomprises exchanging heat on both the cooling side and the heating side.63. The method of claim 49, further comprising sinking heat from atleast one side of the thermoelectric array.
 64. The method of claim 49,further comprising the step of subjecting the thermoelectric elements toat least one magnetic field.
 65. The method of claim 49, wherein themedium comprises at least one fluid.
 66. The method of claim 49, whereinthe medium comprises at least one solid.
 67. The method of claim 49,wherein the at least one medium comprises a combination of at least onefluid and at least one solid.
 68. The method of claim 51, wherein thestep of varying comprises dynamically adjusting the at least onecharacteristic through adjustment of the mechanical configuration of thethermoelectric system.
 69. The method of 68, wherein the step ofdynamically adjusting comprises evaluating at least one parameter andadjusting in response to the evaluation.
 70. The method of claim 69,wherein the step of dynamically adjusting proceeds in accordance with analgorithm in response to at least one sensory input indicative of saidat least one parameter.
 71. The method of claim 51, further comprisingthe step of dynamically adjusting the at least one characteristic inresponse to the evaluation of at least one parameter.
 72. The method ofclaim 71, wherein the step of dynamically adjusting proceeds inaccordance with an algorithm responsive to at least one sensory inputindicative of said at least one parameter.
 73. A thermoelectric systemfor use with a at least one medium to be cooled or heated, comprising:means for forming a plurality of thermoelectric elements into athermoelectric array with a cooling side and a heating side; wherein theplurality of thermoelectric elements are substantially thermallyisolated from each other in at least one direction across the array; andmeans for exchanging heat from at least one side of the thermoelectricarray in a manner that significantly maintains the thermal isolation ofthe thermoelectric elements.
 74. The thermoelectric system of claim 73,wherein the at least one medium moves across at least a portion of atleast one side of the array in at least one direction.
 75. Thethermoelectric system of claim 74, wherein at least one characteristicof the thermoelectric elements is varied in the direction of mediummovement.
 76. The thermoelectric system of claim 75, wherein the atleast one characteristic comprises the resistance of at least some ofthe thermoelectric elements.
 77. The thermoelectric system of claim 75,wherein the at least one characteristic comprises the current through atleast some thermoelectric elements in the array.
 78. The thermoelectricsystem of claim 74, wherein the means for exchanging heat comprises aheat exchanger.
 79. The thermoelectric system of claim 78, wherein theheat exchanger is configured with a plurality of portions each inthermal communication with at least one thermoelectric element, at leastsome portions of the heat exchanger substantially thermally isolatedfrom other portions of the heat exchanger in the direction of mediummovement.
 80. The thermoelectric system of claim 79, wherein at leastsome of the portions comprise posts.
 81. The thermoelectric system ofclaim 79, wherein at least some of the portions comprise fins.
 82. Thethermoelectric system of claim 79, wherein at least some of the portionscomprise heat pipes.
 83. The thermoelectric system of claim 73, furthercomprising a means for sinking heat from at least one side of thethermoelectric array.
 84. The thermoelectric system of claim 73, whereinthe medium comprises at least one fluid.
 85. The thermoelectric systemof claim 73, wherein the medium comprises at least one solid.
 86. Thethermoelectric system of claim 73, wherein the at least one mediumcomprises a combination of at least one fluid and at least one solid.87. The thermoelectric system of claim 75, wherein the at least onecharacteristic is varied by dynamic adjustment.
 88. The method of claim87, wherein the dynamic adjustment proceeds in accordance with analgorithm in response to at least one sensory input indicative of atleast one parameter.